Actually, the riser is 13 feet tall and the vortex cap weighs about 1,000 pounds. We had a hole cut in the top (and finished off with a traffic grade grate) so that we could access the riser for cleaning. We think the beaver are swimming up under the cap and depositing debris down the pipe. But I'm still wondering about the efficacy of the pond levelers for our particular situation. Would they fool the animals as they attempt to stop the flow of water?